I'm planing to load huge text document to textArea for
editing so I need to find a way to page the document.For example if
my textArea in 700px high how to split document to pages and than
to be able to change pages of the document in that textArea?

You'll need to determine the text metrics for some sample
text to know approximately how much room (in pixels) a single line
of text will hold. Then you can determine how many lines 700 pixels
can hold. But since the TextArea does word-wrapping, it may be hard
to determine exactly where the break should come, but you ought to
get close.